CN117377872A - HTCC antenna for generating plasma - Google Patents

Abstract

A plasma generating device for generating a plasma includes a support having a first side and an opposite second side. The support is composed of a ceramic matrix and the split ring conductor is embedded in the ceramic matrix. A hermetically sealed via extends from the split ring conductor to the second side of the support and is connected to a power source. A ground plane is formed on the second side of the support. A plasma is generated proximate to the first side of the support and the support is sealed to the wall of the chamber such that the first side is exposed to the one or more gases inside the chamber and the second side is isolated from the plasma and the one or more gases inside the chamber.

Description

HTCC antenna for plasma generation

Cross-references to related applications

This application claims the benefit of and priority from U.S. Provisional Patent Application No. 63/124,401, filed on December 11, 2020, which application is incorporated herein by reference in its entirety.

Technical field

The present invention relates generally to the field of electrical antennas for igniting and sustaining plasmas, and in particular, wherein the electrical antennas are components of gas sensors that utilize spectral analysis of plasma emissions to determine the properties of a gas mixture.

Background technique

Semiconductor processing tools require ultra-clean wafer processing chambers that maintain tight control over the large volumes of gases used or generated during wafer processing. Accurately measuring the composition of these process gases is important to the operation of machining tools. Accurate measurement of process gases helps optimize process recipes and also provides end-point control. Another factor in ensuring ultra-clean wafer processing is the rapid detection and location of leaks in semiconductor processing tools. Additionally, to maintain product yield and quality, it is also important to characterize background contaminants such as water or hydrocarbons after scheduled maintenance.

Many semiconductor tools use plasma to facilitate deposition and etch processes. For example, plasma is necessary for most sputter deposition processes and also plays a role in plasma-enhanced atomic layer deposition, plasma-assisted chemical vapor deposition, and most etching processes. The light emitted directly from these plasmas is sometimes monitored through windows in the process chamber to enable the quality control measurements mentioned above using a method called optical emission spectroscopy (OES). However, it is sometimes desirable to monitor gases in a processing chamber when the plasma source is not enabled, or in a chamber in which the plasma source is not used, such as a buffer/transport or degassing chamber. In other cases, the plasma source may be positioned away from or remotely located within the process chamber so that only chemical products enter the process chamber. Therefore, for the cases mentioned above, it is not always possible to use the plasma source of the processing chamber to analyze the process gas.

In some cases, gases and leaks can be monitored with mass spectrometry-based residual gas analyzers. Unfortunately, mass spectrometers require lower operating pressures than those used during most semiconductor processing. Therefore, in order to use mass spectrometry, additional aspiration is required to reduce the sample pressure for analysis. This extra pumping increases cost and slows down the system's response time. Additionally, the ion-optical lens system of a mass spectrometer is particularly susceptible to damage from the deposition of many thin films used in building semiconductor devices. Even very thin dielectric layers can cause charge buildup, which degrades spectrometer performance and can prevent mass spectrometers from operating.

An alternative to mass spectrometry or monitoring process plasma is to use a sensor that provides its own plasma source. Such sensors may operate in a manner similar to the plasma OES measurements described above, but may be installed in a chamber without a plasma source, or may be used during times when the internal plasma source is not operating. This type of sensor is referred to below as a self-plasma-OES (SP-OES) sensor. (See for example US7309842, US7123361, WO10129277A2, US20200273676 and US10262841. See also https://products.inficon.com/en-us/nav-products/product/detail/p-quantus-lp100/,

http://www.nanotek.com/eng/products/products.php? ptype=view&prdcode=1608050006&catcode=181000&page=1&catcode=181000&searchopt=&searchkey=).

These sensors (INFICON Quantus LP-100, Nanotek AEGIS, etc.) are capable of operating at pressures between approximately 1e-3mbar and approximately 1mbar. This pressure range covers some semiconductor processes, however, many processing chambers operate above this pressure range during at least some portion of the process. For example, important processes like ALD and CVD typically operate at tens of millibars. Generating plasma at lower pressures takes advantage of longer electron mean free paths (e.g. about 380 μm or more for pressures below 1 mbar) in order to impart sufficient energy to the electrons for ionization using fairly low electric fields. gas molecules, thereby producing the desired plasma. For example, the first ionization energy of argon (Ar) is 15.8 eV. Therefore, if electrons are to cause ionization of argon, the electric field must be high enough to impart that much energy to the free electrons between collisions with surrounding gas molecules. This shows that the electric field required to ionize argon at 1 mbar pressure is 15.8eV/(e*380μm) or 41.6kV/m (where e is the magnitude of the charge on the electron). As the pressure is reduced, the average path length traveled by electrons between collisions with the background gas increases, and therefore the energy they gain between collisions increases for a given electric field. Therefore, lower pressure requires a lower electric field to hit the plasma. This also means that generating plasma at higher pressures typically requires higher electric fields to obtain ionization energy over a much shorter mean free path. For example, ionizing Ar at 50 Torr would require about 2E6V/m, since the mean free path of electrons at that pressure is only about 8μm, and 15.8eV would still be needed to ionize Ar.

Several methods have been investigated to generate microplasmas that can operate at higher pressures (these plasmas are often referred to as microplasmas because they typically have a characteristic length of less than about 1 mm). These methods include DC discharge, high frequency AC discharge, and also microwave discharge. For example, a microwave resonant circuit including an antenna in the form of a microstrip split ring resonator is one such approach. US Patent No. 6,917,165 to Hopwood discloses the construction of a microwave microstrip resonator in the shape of a ring (with a small gap at the ends of the resonator) or a split ring resonator. The structure is patterned with metal onto a thin dielectric substrate with a metal ground plane on the opposite side of the dielectric substrate. The resonant frequency is determined by the ring circumference such that this length corresponds to half the wavelength in the conductor. The impedance is set by the location along the resonator where the resonator is driven and the characteristic impedance of the microstrip. Driving the resonator with a small low power RF amplifier (such as those now available for telecommunications and Bluetooth) generates potentials at the resonator ends that are 180° out of phase with each other. This creates an electric field near the resonator gap that is sufficient to ignite and sustain microplasmas in many gases and at pressures ranging from below 1 mbar to as high as and slightly above 1000 mbar. Microplasmas have many potential uses, including disinfection and as a controlled light source. In one application, the plasma source may be exposed to the process gas in the SP-OES.

Split-ring resonators, as well as many other types of high-voltage plasma sources with exposed electrodes, suffer from limited lifetime problems because the ends of the resonators are quickly eroded by the plasma itself. This erosion reduces the electric field generated when the geometry of the ends of the split ring resonator changes. Changes in tip geometry also lead to changes in electrical properties such as resonant frequency and impedance. Another disadvantage of split ring resonators is that material from corroded split ring conductors may be redeposited onto other areas of the dielectric substrate, which reduces the resonator's quality factor. When the quality factor decreases, the maximum electric field generated decreases, which reduces the efficiency of the plasma source and also reduces the pressure range within which the plasma source can operate. The material of the split ring conductor may also be redeposited onto the window used to collect light for the OES, resulting in an undesirable loss of collected light. Additionally, sputtering open-ring conductors into semiconductor processing chambers is unacceptable. Contamination of the process with this sputtered material can destroy the produced wafers. Sputtering of conductors can also form particles that can damage some semiconductor processes.

Covering the device antenna with a thin layer of dielectric such as glass has been shown to prevent erosion of the loop. However, varying thermal expansion and chemical incompatibilities prevent the use of most glasses in semiconductor processes. Maximum temperatures and process chemicals further prevent the use of materials like silicone glass or polyimide plastic that might be used to cover the resonators. Additionally, certain metals should never be exposed to the semiconductor process due to the risk of poisoning the process. For example, even ultra-trace amounts of gold or copper from a sensor can damage the electrical properties of the silicon wafer it processes that is being monitored. As a result, conductor materials must be fully encapsulated in a manner that isolates them from the processing chamber, even under conditions of excessive temperatures and/or exposure to etching chemicals.

For sensors designed to operate in the harsh environments of the semiconductor industry, there are limitations in the wetting materials that are considered acceptable. Processes such as etching and chamber cleaning use corrosive gases such as nitrogen trifluoride ( _NF3 ) and high process temperatures that can range above 400°C. Therefore, any sensor must be designed to prevent unacceptable material exposure to the semiconductor process while being robust enough to withstand the harsh conditions of the semiconductor process. Covering plasmon-generating antennas with most silicon-containing glasses fails because these glasses are rapidly eroded by etching gases configured to remove silicon (eg, _NF reacts with Si to produce volatile silicon tetrafluoride ( _SiF )). Thin coatings (tens of nanometers) on antennas with ALD aluminum oxide cannot withstand most semiconductor processes. Alternatively, thick aluminum oxide coatings on the antenna (such as plasma spraying) suffer from adhesion problems. If thick aluminum oxide coatings fail, the release of aluminum oxide particles can damage semiconductor tools and process wafers. Furthermore, the plasma source antenna must be low enough in cost that it can be easily replaced in the field.

There are additional problems for measurement systems designed to operate at pressures from about 1 mbar to about 1000 mbar. In this pressure range, the mean free path of the gas molecules is typically very short relative to the size of the sensor. If the gas cell housing, plasma source, and window for light collection are constructed such that the gas being monitored must travel long distances to enter and exit the gas cell, the sensor will not respond quickly enough to resolve the semiconductor issue due to diffusion limitations. Some common problems in industry. For example, one type of leak may occur when a slit valve is briefly opened to allow a wafer to move from the transfer chamber and into the processing chamber. Such leaks may be short-lived and require a rapid response to detect this leak and identify the source. Therefore, it is important to design a sensor that communicates tightly with the process environment with minimal intervening channels.

These are just some of the issues associated with currently used self-plasmonic-OES sensors, especially for monitoring semiconductor processing tools.

Contents of the invention

The present disclosure relates to a sensor that is directly exposed to the process environment with minimal intervening channels. An embodiment of the plasmon generating source includes a split ring resonator microstrip including a split ring conductor and a ceramic dielectric matrix. The dielectric matrix is configured to support split ring resonator microstrips with the split ring features embedded within the ceramic matrix. In embodiments, the dielectric consists primarily of _Al2O3 or other _process compatible material. In an embodiment, the split ring conductor is composed of a refractory metal. In an embodiment, the ceramic matrix is hermetic and configured to isolate the split ring conductor from the process, and the plasma generation source is sealed at the front. The plasma generation device may further include a light collection element configured to protrude from the flange. In an embodiment, the light collection element is a collimating lens positioned proximate the open ring conductor and includes a curvature configured to match the plasma light to the input field of view of the fiber or spectrometer.

An embodiment of a plasma generation device for generating a plasma from one or more gases inside a chamber includes a support including a ceramic matrix and having a first side and an opposing second side. The split ring conductor is embedded in the ceramic matrix, and a hermetically sealed via extends from the split ring conductor to the second side of the support. An airtight via is configured to connect to a power source, and a ground plane is formed on the second side of the support. The plasma is configured to be generated proximate the first side of the support. The support is configured to seal to the wall of the chamber such that a first side is exposed to one or more gases inside the chamber and a second side is isolated from the plasma and one or more gases inside the chamber.

In embodiments, the ceramic matrix is composed of at least one of Al ₂ O ₃ and AlN. In embodiments, the ceramic matrix is composed of one or more materials that are compatible with the plasma and one or more gases inside the chamber. In an embodiment, the split ring conductor is composed of a refractory metal. In another embodiment, a plasma generating device includes at least one plasma initiating electrode, wherein each electrode includes a hermetically sealed via extending through the ceramic matrix from a first side of the support to a third side of the support. Two sides. In an embodiment, the at least one starting electrode is composed of a refractory metal. In yet another embodiment, the plasma generating device includes a plurality of initiating electrodes spaced apart with respect to each other by a predetermined distance to enable initiating the plasma within a predetermined pressure range such that the activation between the electrodes The distance may be increased or decreased depending on the pressure range that the plasma generating device will use to generate the plasma.

In an embodiment, the plasma generation device further includes a light collection element spanning the ceramic substrate and the ground plane. The light collection element is configured to collect light emitted by the plasma and transmit the light through the ceramic matrix and the ground plane for viewing from the second side of the support. The light collecting element is hermetically sealed against the ceramic matrix. In an embodiment, the light collecting element is a lens positioned proximate to the split ring conductor. In an embodiment, the lens includes a curvature configured to optimize transmission of the light to an input field of view of one of: (1) an optical fiber; (2) an optical fiber bundle; and (3) a spectrometer.

An embodiment of the gas sensor includes a split ring resonator microstrip including a split ring conductor surrounded by a ceramic matrix and configured to generate a plasma. Optical elements configured to collect plasma light penetrate via holes in the ceramic matrix. The optical element is hermetically sealed to the ceramic matrix using one of a braze seal and a compression seal, and the ceramic matrix includes alumina. In an embodiment, the optical element includes sapphire. Sapphire can be constructed into thermally matched ceramic matrix alumina and split ring conductors. In an embodiment, the optical element includes a lens shape. In an embodiment, the optical element includes a light pipe. The light pipe may terminate at an angle configured to accept light from near the center of the ends of the split ring resonator and direct the light through the split ring resonator. In another embodiment, the gas sensor further includes an antenna connection configured to receive RF energy from the cable and transmit light out through the fiber. In an embodiment, the gas sensor is configured to operate with remote electronics and to operate at temperatures above 120°C. In an embodiment, the gas sensor is configured to be mounted directly into the test chamber. In another embodiment, the gas sensor further includes a plasma shield and a light baffle.

An embodiment of the gas sensor includes a plasma generating device having a first side and an opposing second side. The plasma generating device includes a split ring conductor surrounded by a ceramic matrix and configured to generate plasma proximate the first side. An optical element extends through the ceramic matrix between the first and second sides and is configured to collect light emitted by the plasma. The connector is electrically connected to the split ring conductor. The optical element is hermetically sealed to the ceramic matrix using one of the following: (1) a braze seal; and (2) a compression seal.

In an embodiment, the connector of the gas sensor is an antenna connector configured to receive RF energy from the cable, and the optical fiber is connected to the optical element and configured to receive light collected by the optical element. In embodiments, the gas sensor further includes remote electronics configured to interact with the gas sensor via cables and optical fibers, wherein operation occurs at temperatures above 120°C. In embodiments, the plasma generation device is configured to be exposed to one or more gases within the processing chamber and serve as part of a wall of the processing chamber. In an embodiment, the first side of the plasma generation device includes a polished surface.

An embodiment of a method of fabricating a split ring resonator microwave plasma source includes patterning a stack of ceramic strips with conductors using a screen printing process to create a hermetically sealed antenna that includes conductor traces. In another embodiment, the method further includes polishing the fired dielectric on the resonator electrode. In another embodiment, the method further includes adding witness marks to the conductor trace layer. During the cutting process, index marks are exposed and used to guide polishing to the target thickness.

Another embodiment of a method of manufacturing a plasma generating device includes forming a support from a ceramic matrix in a green state, wherein the support includes a first side and an opposing second side. During formation of the support, a split ring conductor and a hermetically sealed via are embedded in the ceramic matrix, with the via extending from the split ring conductor to the second side of the support. The ceramic matrix with the embedded split ring conductor is then fired, and the ground plane is positioned close to the second side of the support before or after firing. The first side of the support is polished to obtain a desired thickness of the ceramic matrix between the first side and the split ring conductor, wherein the desired thickness of the ceramic matrix corresponds to the desired resonant frequency.

An embodiment of a self-plasma emission spectroscopy (SPOES) system includes a plasma generating device and a temperature sensor in thermal communication with the plasma generating device to determine a temperature of the plasma generating device. The temperature of the plasma generation device is taken into account during operation of the SPOES system. In an embodiment, the SPOES system further includes a heater in thermal communication with the plasma generation device. The heater and temperature sensor are configured to control the temperature of the plasma generating device. In another embodiment, a SPOES system includes a plasma generation device and a light collection device, a VCR gland, and One of the flange and the KF flange in which the plasma generation device and the light collection device are soldered to the VCR gland,/> flange and one of the KF flange. In an embodiment, the dual-connection flow-through gas unit is configured such that the gas flow is largely parallel to the plane of the antenna and optical window, and wherein the gas channel or plasma chamber features are largely normal to the gas flow. None are larger than about 10mm in any of the main directions.

An embodiment of the gas sensing system includes a plasma generation device including a split ring resonator microstrip. The split ring resonant microstrip includes a split ring conductor and a ceramic matrix configured to surround and support the split ring conductor. A temperature sensor is in thermal communication with the plasma generating device to determine the temperature of the plasma generating device such that the temperature of the plasma generating device is taken into account during operation of the gas sensing system. In an embodiment, the gas sensing system includes a heater in thermal communication with the plasma generating device. In this embodiment, the heater and temperature sensor are configured to control the temperature of the plasma generating device.

Another embodiment of a gas sensing system includes a plasma generation device including a split ring resonator microstrip. The split ring resonator microstrip includes a split ring conductor and a ceramic matrix configured to support the split ring resonator microstrip. Split ring conductors are embedded in a ceramic matrix. In an embodiment, the gas sensing system further includes a dual-connection flow-through gas cell defining a gas channel through the plasma chamber. The optical window is positioned generally across the plasma chamber from and parallel to the ceramic matrix of the plasma generating device. The gas unit is configured to provide gas flow in a direction generally parallel to the plane of the plasma generation device and the plane of the optical window. The gas channels and plasma chamber are composed of features with dimensions less than about 10 mm along a direction generally normal to the direction of gas flow.

High-temperature co-fired ceramics, or HTCC, is a process used to produce metal and ceramic parts. In this process, the green ceramic tape is built up into many layers. Between any of these layers, a metallization made of a refractory metal can be used to define a split ring resonator electrode. This metallization can be patterned by screen printing, inkjet printing, or using any other typical HTCC metallization process. The green material and metallization are then fired at temperatures above 1200°C to sinter the material and remove the binder. Constructed in this way, the metallic features of the split ring resonator are completely embedded in the ceramic, except for the connection to a single via coming out of the ceramic through the backside (the side opposite to the side where the plasma is generated). An electrical connector is attached to the via so that RF power can be delivered to the resonator from an appropriate power supply. By mounting the resonator or antenna on a chamber that keeps vias and connectors out of the process, all parts of the gas sensor that are then exposed to the process can withstand certain semiconductor processing, including withstanding high temperatures and corrosive chemicals. substance. These parts of the device can be made to withstand temperatures above 1200°C by using split ring conductors made of refractory metals such as tungsten and dielectrics made of aluminum oxide. Operation at temperatures above 300°C requires a metal seal (such as a C-seal or wire seal) to seal the antenna to its sensor chamber, or to the flange in the absence of a sensor chamber. Because the antenna is constructed from high-temperature materials, it is also compatible with the soldering process, enabling soldered windows and soldered connections.

Description of the drawings

The invention briefly summarized above may be described in greater detail by reference to the described embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Accordingly, for a further understanding of the nature and objects of the present invention, reference may be made to the following detailed description, which is read in conjunction with the accompanying drawings, in which:

Figure 1 illustrates a top view of an embodiment of a plasma generation device;

Figure 2 illustrates a top plan view of an embodiment of a wafer comprised of the plurality of plasma generation devices of Figure 1;

3A illustrates a partial cross-sectional view of the plasma generation device of FIG. 2 along line G-G;

Figure 3B schematically illustrates a close-up view of a cross-section of an embodiment of a plasma generation device;

4 illustrates a cross-sectional view of an embodiment of a gas unit assembly including an embodiment of a plasma generation device;

5A illustrates a cross-sectional view of another embodiment of a gas sensor assembly having an embodiment of a plasma generation device;

5B illustrates a cross-sectional view of an embodiment of a gas sensor having an embodiment of a plasma-generating HTCC antenna;

Figure 5C illustrates an enlarged schematic view of a portion of the embodiment of the gas sensor assembly of Figures 5A and 5B;

Figure 6 illustrates a schematic representation of an embodiment of a shielding element;

Figure 7 illustrates a schematic diagram of an embodiment of a gas cell assembly having an embodiment of a plasma generation device and connected to an amplifier and spectrometer or filter-photodiode system;

Figure 8 illustrates a cross-sectional view of an embodiment of a gas cell assembly with an embodiment of a plasma generation device, where there are both inlet and outlet connections for gas flow;

Figure 9A illustrates a perspective top view of another embodiment of a plasma generation device;

Figure 9B schematically illustrates a cross-sectional view along line H-H of the embodiment of Figure 9A.

Figure 10 illustrates a perspective top view of another embodiment of a plasma generation device;

Figure 11 illustrates a perspective top view of the embodiment of the plasma generation device of Figure 10 with a portion removed; and

Figure 12 illustrates a perspective side view of the embodiment of the plasma generation device of Figure 10.

Detailed ways

The following discussion relates to various embodiments of HTCC antennas for generating plasma or microplasma. It will be understood that the embodiments described herein are examples that illustrate certain inventive concepts as detailed herein. To this end, other variations and modifications will be apparent to the skilled person. Additionally, certain terminology is used throughout this discussion in order to provide a suitable frame of reference with respect to the drawings. Words like "up", "down", "forward", "backward", "inside", "outside", "front", "back", "top", "bottom", "inside", "outside" The terms "first," "second," etc. are not intended to limit these concepts unless specifically indicated where they are. The term "about" or "approximately" as used herein may refer to a range of 80% to 125% of the claimed or disclosed value. With regard to the drawings, their purpose is to depict the salient features of the HTCC antenna for generating plasma or microplasma and are not specifically provided to scale.

Referring to FIGS. 1-3 , an embodiment of a microwave microstrip antenna used herein as plasma generation device 100 is configured to form a high electric field or electromagnetic wave that interacts with the surrounding environment to generate plasma, as indicated by circle/ellipse 400 . The generated plasma 400 serves as a source of light with a spectrum that depends on the composition of the gas mixture used to generate the plasma and other factors. Analysis of this spectrum can be used to determine the composition of the surrounding ambient gases. In this way, the presence of unwanted gases or vapors can be detected.

The plasma generation device 100 includes antenna traces 110 embedded in a dielectric support composed of a ceramic matrix 150 . In an embodiment, ceramic matrix 150 is a high temperature co-fired ceramic (HTCC) matrix. As used herein, the terms "encapsulated" and "embedded" when used to refer to the location of antenna traces 110 relative to ceramic substrate 150 mean that antenna traces 110 are completely enclosed within the ceramic substrate. 150 such that no portion of antenna trace 110 is exposed. Referring to FIG. 1 , antenna trace 110 is shown in dashed lines, indicating that it is embedded within ceramic matrix 150 , however in some embodiments, antenna trace 110 may still be visible through ceramic matrix 150 , although no portion thereof is exposed. In an embodiment, antenna trace 110 is a split ring conductor or split ring resonator. Antenna trace 110 may operate at a specific frequency at which it resonates (eg, 2.45 GHz). The choice of frequency will affect the size of the antenna trace 110. The antenna trace 110 defines a slit or gap 107 having a width that spans the distance between the two ends of the antenna trace 110 . Gap 107 may vary in width, but is generally preferably in the range of 25 to 100 microns. A high electric field is generated in a region within or near gap 107 and may induce the formation of plasma 400 in a region near gap 107 , such as a region above gap 107 . In this embodiment, gap 107 is completely filled with ceramic matrix 150 and plasma generation occurs close to top surface 130 of first side 101 . In embodiments, the conductors of antenna traces 110 may be composed of tungsten, and the HTCC matrix may be composed of aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), or other similar materials. Embedding the antenna trace 110 in the ceramic matrix 150 serves to isolate it from the corrosive environment that may be present in the process chamber.

Although the term "ring" has been used with reference to certain embodiments of antenna trace 110, the term is not meant to be limited to circular rings, but may include all circular and non-circular shaped resonators, such as rectangular, elliptical and Other shapes.

Plasma generation device 100 may be formed on wafer 200 as illustrated in FIG. 2 . Each plasma generation device 100 has a support comprised of a ceramic matrix 150 having a first side 101 , a process side or a plasma side that when in use will be exposed to a semiconductor production process or processing chamber, and is protected or A second side 102, a non-process side or a non-plasma side that is not otherwise exposed to the semiconductor process or processing chamber (FIG. 3A). During metallization of antenna trace 110, features 120 are added at the same level during the HTCC stacking process. These will act as guides or position indicators during the final polishing step discussed later. The plasma generating device 100 is fired and then cut from the wafer to form individual devices into sliced squares 112 as illustrated in FIG. 1 or laser or water jet cut into the desired shape (e.g., as Circle 114 as shown in Figure 2, or other shape as desired). Cutting of plasma generation device 100 occurs through feature 120 . Feature 120 is positioned to be cut through during the cutting process and is shown in dashed lines in FIG. 1 , indicating that it is positioned within ceramic matrix 150 , however in some embodiments, feature 120 may be visible through ceramic matrix 150 .

3A-3B illustrate a cross-section along line G-G of one of the plasma generation devices 100 on the wafer 200 of FIG. 2 . As shown, antenna traces 110 are embedded in HTCC matrix 150 . Feature 120 is exposed at the edge of plasma generation device 100 after the slicing or cutting process and serves as a guide for measuring the thickness 152 of ceramic substrate 150 over antenna trace 110, as shown in the schematic cross-section in Figure 3B is better seen. As shown, antenna traces 110 and features 120 are positioned at the same distance from the top surface 130 or front surface. In other words, plane P extends through both antenna trace 110 and feature 120 such that they are located at the same depth within ceramic matrix 150 relative to top surface 130 . Strict control of the thickness 152 of the ceramic matrix disposed over the conductor traces 110 is necessary to obtain the desired resonant frequency and generate the high electric fields necessary to form the plasma 400 . Top surface 130 is polished down until features 120 are at a target thickness (or distance) from top surface 130 and therefore conductor traces 110 are at the same target thickness (or distance) from top surface 130 . In an embodiment, feature 120 is a location-indicating mark (such as a flat portion or a protrusion).

For example, with an RF power of 33 dBm and an antenna gap 107 of 100 microns, when the thickness 154 from the top surface 130 to the position indicator mark 120 is 0.001 inches, sufficient electric field is generated to form the desired plasma 400 while still Provides good etch resistance and sputter resistance, allowing the antenna trace 110 to last for many years. In contrast, when the thickness 154 between the top surface 130 and the index mark 120 is less than 0.001 inches, the resulting antenna trace 110 is not well protected. However, when thickness 154 is significantly greater than 0.001 inches, the desired high electric fields in the gap are suppressed. Other techniques for assessing the thickness 154 of the ceramic matrix 150 between the top surface 130 and the index mark 120 , such as optical interferometry or spectral reflectance, typically fail due to the opaque optical quality of the ceramic matrix 150 . Thickness 154 may allow antenna traces 110 (and location markers 120 ) to be visible through ceramic matrix 150 even though antenna traces 110 are embedded within ceramic matrix 150 .

A ground plane 160 is positioned on the back or non-process side 102 of the ceramic substrate 150 to complete the plasma generation device 100 . In embodiments, ground plane 160 may be positioned before or after the plasma generation device is sintered. Ground plane 160 is the ground reference and includes an adhesion layer such as titanium, followed by a plating layer of highly conductive material such as gold. This area is not exposed to the semiconductor process because the seal is formed between the outer edge of the ceramic substrate 150 or to the top surface 130 of the ceramic substrate 150 (Figures 3A, 3B, and 4) and the cell chamber 408 where the plasma will be generated and observed. (Fig. 4). Filled via 172 electrically couples antenna trace 110 to pad 170 (FIG. 3A) at feed point 174 (FIG. 1). Pad 170 is positioned generally at the same level as ground plane 160 but is electrically isolated from ground plane 160 . Additionally, a ring 173 of nickel or other suitable metal may be plated over the adhesion layer for use in forming a solder connection to the housing or flange. In the case of a circular device, the feature may alternatively be on the outer cylindrical surface of the plasma generation device 100 . In some embodiments not yet described that include a soldering process, electroplating or gold or copper metallization of ground plane 160 should occur after the soldering step so that the ground plane is not damaged by high soldering temperatures.

FIG. 4 illustrates a cross-section of a gas cell assembly 429 including the plasma generation device 100 . Gas unit assembly 429 is configured to connect to a semiconductor processing chamber, degassing chamber, or transfer chamber. As shown, the process side 101 of the plasma generation device 100 becomes the wall of the cell chamber 408 such that if not for the ceramic matrix 150 surrounding it, the encapsulated split ring conductor or antenna trace 110 would be in the gas cell assembly 429 inside or otherwise exposed to the unit chamber 408 . RF energy is delivered through connector 406 soldered to via 172 in plasma generation device 100 to cause plasma generation device 100 to resonate and deliver the power required to ignite and sustain plasma 400 in cell chamber 408 . The unit chamber 408 is connected to the process chamber being monitored via a process connection flange 420, which may be KF-25 (although other flange types may be used). Optical baffle 410 protects plasma generation device 100 from other light sources and protects other photosensitive components of the semiconductor processing chamber from light generated by plasma 400 without significantly impeding gas flow. Cell chamber 408 has dimensions from about 5 mm to about 20 mm, which is sufficient to contain plasma 400 at most process pressures of interest (eg, between about 1 Torr and 50 Torr). The seal is made from O-rings 431 and 432, which are positionable in O-ring groove 409. A window 405 is provided to enable light to exit the unit chamber for spectral analysis. In some semiconductor tool installations, baffle 410 also reduces deposition of process material on window 405 from the process being monitored. Unit room 408 can be made of stainless steel, Aluminum or/> or any other compatible material. Clamp 444 presses plasma generation device 100 against O-ring 431 to form a gas-tight seal, and also acts as a heat sink to reduce changes in plasma impedance, or after extinguishing or activating the plasma, or in tool formulation. The thermal expansion or contraction of the plasma generation device 100 results from the change. This thermal change will change the characteristic impedance and resonant frequency of the plasma generation device 100, which can reduce the quality factor and prevent efficient operation, prevent the plasma from restarting, or can cause the signal to drift. Clamp 444 may be formed from stainless steel or a more thermally conductive material such as aluminum or copper.

For some pressures and processes, isolation of the plasma 400 provided by locating the unit chamber 408 of the plasma generation device 100 away from the process connection flange 420 is desirable. However, for other processes and pressures, such as when the pressure is above 1 Torr and the process to be measured changes rapidly (<10 s), then the tortuous path to the plasma 400 is unsuitably long. The ratio of the mean free path of molecules in a gas to the characteristic system size is called the Knudsen number Kn. When Kn is greater than 1, gas molecules collide with the chamber walls before colliding with each other, and the flow is considered a molecular flow. When Kn is between 1 and 0.01, the flow state is considered transitional, and when Kn is less than 0.01, the collisions of gas molecules with each other are much greater than the collisions with the chamber walls, and the flow is called a viscous flow. If the mean free path of the gas is much shorter (low Kn) than the dimensions of the sensor cell chamber and connected components, then the time-dependent gas composition in the cell chamber lags that in the process chamber being monitored, and an effective sensor response Time is too slow to be useful. For example, under typical atomic layer deposition (ALD) process conditions of an argon support at 40 Torr, the mean free path of a typical reagent molecule will be less than 1 μm from the process connection flange 420 to the plasma 400 location in the gas cell assembly 429 The path length is approximately 7cm. This would mean that if a gas is flowing, it will be a viscous flow. However, for a dead-end arrangement as in the gas cell assembly 429, any changes in the gas composition of the process being monitored will be transmitted to the plasma volume only by diffusion, with a time constant on the order of many seconds, which in particular depends The square root of the molecular mass of the diffusing species and the process temperature. Therefore, this would be too slow for monitoring many modern semiconductor processes such as ALD with sub-second duration gas pulses and sub-10 second pump out times.

5A-5C illustrate another mounting arrangement of the plasma generation device 100 that is intended to provide better response time to chamber pressure where the mean free path is shorter than the size of the unit chamber 408. can be or other metal ring 189 soldered to the edge of the plasma generation device 100 and subsequently welded or brazed to the flange 191 . Brazing materials having a melting point of approximately 780°C may be used, such as silver-copper alloys. In other embodiments, higher temperature brazes may be used, such as 35:65 gold-copper alloy brazes. Brazing on the backside provides the added benefit of isolating these materials from the plasma 400 . As shown in Figure 6, shielding elements 701, such as steps in the edge of the plasma generation device 100, may be used to prevent the plasma from reaching the braze metallization 702. This feature may be built into the stacked layers of ceramic tape used to form the plasma generating device 100 prior to firing, or alternatively may be ground into the plasma generating device 100 after firing by ceramic machining.

In one embodiment, rather than using a window separate from the plasma generation device to collect light, a window, light pipe, light collection element, or other light collection device may be sealed by the ceramic matrix 150 of the plasma generation device 100 (via soldering). welding, compression sealing or other attachment process). The holes are laser cut after sintering, but can also be punched in the green ceramic tape during the manufacturing method described later. A light collecting device can be installed in this hole. Including the light collection device in the plasma generation device enables the plasma generation device 100 to be mounted directly into the processing chamber or transfer chamber, resulting in faster response times and allowing the use of a single port on the processing chamber 500 or tool chamber. Install. No separate light collection device (window) is required, allowing for a much more compact SP-OES system sensor. Although O-ring seals are possible with this geometry, they do not allow for the high temperature operation desired by some applications. Still referring to FIGS. 5A-5C , the window or light pipe 300 may be ground to collimate light for efficient transmission into a fiber, fiber bundle, or spectrometer, or the window 300 may include a first end 320 and a second end 330 . The first end 320 may be cut at an angle to reflect light from the plasma 400 through the plasma generation device 100 and act as a light pipe defining an outer surface 321 and configured to efficiently transmit light into the optical fiber connector 504 . Optical element 505 may improve optical coupling of collected light into the spectrometer. The use of sapphire optics allows the use of brazing operations and thermal expansion matched to the plasma generation device 100 (for high temperature operation) and the transmission of light with wavelengths from 200 to 2000 nm. Connection to the flange of chamber 500 is made at 191 . O-ring and aluminum knife edge seals are possible with this KF flange, but other flange configurations are also possible, such as VCR and They typically utilize all metal seals for high temperature operation.

Figure 7 illustrates a processing chamber 500 at least partially surrounded by a processing chamber wall 510 with a flange of the SP-OES sensor mounted to a flange on the chamber 500. This allows the plasma generation device 100 to be mounted so that it is adjacent to, flush with, or inserted into the chamber 500 , which eliminates any delay due to diffusion into the gas cell assembly 429 (if that is used) . The plasma generation device 100 in this configuration is immersed in a semiconductor manufacturing process. An RF compatible connector 503 is used to introduce RF energy into the plasma generating device, and a fiber optic connector 504 is used to transmit the plasma generated light out. Amplifier 501 generates microwave frequency energy, and section 502 contains a spectrometer or filter-photodiode system for measuring light from the process gas in plasma 400 . The spectrometer is configured to measure light intensity as a function of wavelength within a certain range (eg, 200-850 nm). From these spectra, information can be obtained about the composition of the gases in the plasma. Alternatively, if only a specific known waveband is of interest, the plasma light can be monitored using a filter that passes that band and a photodiode or photomultiplier. The cable arrangement 532, 534 allows the plasma generation device 100 to be installed in a limited space, and the electronics and spectrometer or photodiode to be mounted at a distance such that the electronics and spectrometer can be kept appropriately cool, as determined by the component specifications. That is true even when the processing chamber 500 is operating at elevated temperatures. In embodiments, electronics may enable remote operation of gas unit components and/or process chambers.

Figure 8 illustrates another alternative to the appendage geometry depicted in Figure 4. The flow-through cell 600 has a geometry such that gas flows directly from the cell window 620 through the plasma generation device 100, which is positioned across the gas path. The unit is streamlined, with no unswept volume, allowing it to provide rapid response to changes in gas concentration, such as in a flowing gas stream in a gas delivery line or pump line. A limitation of this geometry is that it requires two connections 602, 603, which is undesirable for installation in some other applications.

Another embodiment of the plasma generation device 100A is shown in Figures 9A-9B. Similar to other previously discussed embodiments, conductor traces 110 are surrounded by ceramic matrix 150 . Similar to those embodiments, the plasma generation device 100A includes a first hermetically sealed via 506 for routing power from the solder to the non-process or non-plasma side 102 such as an SMA connector. The RF compatible connector 503 passes partially through the ceramic matrix 150 to the packaged antenna traces 110 of the plasma generating device 100A, which generates an electric field near its end (in the gap 107) to ignite and sustain the plasma. body 400 (Fig. 3A). The gas-tight via 506 is hermetically sealed such that it is gas-impermeable relative to the ceramic matrix 150 . In an embodiment, a second hermetically sealed via 508 extends from a second SMA connector 513 or other suitable high voltage connector also soldered on the non-process side 102 . The second via 508 does not terminate with a buried conductor inside the ceramic matrix 150 , but rather it extends through the process surface of the ceramic matrix 150 with its end exposed to the process environment being monitored as a conductive electrode 514 . The conductive electrode 514 has a sufficient thickness such that after the processing steps are performed, the conductive electrode 514 remains exposed on the surface of the process side 101 of the plasma generation device 100A. For example, a polishing step may be performed to remove an amount of dielectric while still keeping the antenna traces 110 buried under the layer of ceramic substrate 150, but the electrode 514 will remain.

Under certain pressures or gas compositions, the electric field near gap 107 in antenna trace 110 and extending through the dielectric is too low to initiate plasma 400 . In these cases, a high voltage signal, such as a 10 Hz square wave of -3 kV, is applied to the second via 508 through the connector 513 for several seconds. This results in a series of arc discharges between the walls of the processing chamber 500 and the conductive electrode 514 exposed at the top of the via 508 . The arc generates photons, electrons, and ions, and these species reduce the breakdown potential near gap 107 in open ring conductor 110, which allows initiation of plasma 400 over a wider range of pressure and/or gas conditions. Once the plasma 400 is initiated, it can be maintained substantially without continued emission from the electrode 514 .

In some embodiments, second via 508 and conductive electrode 514 are also tungsten like first via 506 and antenna trace 110 . Tungsten is desirable because of its high mass density and low sputter cross section. The second via 508 is positioned so that the arc occurs at the ground wall and is close enough to the gap 107 in the antenna trace 110 to ignite the plasma 400 quickly. At the same time, the second via 508 is positioned far enough away from the gap 107 of the antenna trace 110 that it will not be damaged during the generation of the plasma 400 . In an embodiment, the second via 508 is positioned at a distance of 1 mm from the wall of the process chamber 500 and 7 mm from the gap 107 of the split ring conductor 110 .

In some embodiments, the signal from the photodiode or the signal from an attached spectrometer is analyzed in an FPGA or microcontroller to detect the plasma off state and induce a high voltage waveform at the plasma start electrode 514 . Such a plasma activation device can be added to the plasma generating device 100, 100A at little or no additional cost while still producing a plasma generating device 100, 100A with a low profile. Conventional plasma starters like brazed feedthrough pins are more expensive, and they are more difficult to place near the main plasma source - which is important at high voltages. In some embodiments, more than one additional conductive electrode 514 is added. In this case, the distance between the electrodes 514 and/or between the electrodes and the wall(s) of the processing chamber 500 may be selected to facilitate plasma ignition at different pressures. Knowing the target pressure and gas species, one can read the optimal spacing for a given power source from the Paschen curve of breakdown voltage as a function of distance and pressure, or alternatively, select the power source to suit the available geometric shapes. In embodiments, conductive electrodes 514 include circular or annular shapes and are extensions of their respective vias 508 . In another embodiment, the conductive electrode 514 includes a shape other than a circle or annular shape, such as a star shape, in order to generate a higher electric field. In yet another embodiment, even more electrodes may be included in the plasma generation device 100A and positioned at various distances from each other and from the chamber wall 510 to enable initiation of the plasma over a wider pressure range. 400. They can be driven by multiple connectors and voltage sources. In other embodiments, if the intention is to arc multiple electrodes to a chamber or sensor wall, multiple electrodes may be connected together and driven from the same connector. Each electrode can be located at a different distance from the wall. The only real limitation will be the acceptable size and complexity of the plasma generation device.

A method of producing a plasma generating device 100, 100A such as the previously described embodiment will now be described. Typically, multiple layers of green ceramic tape are used to construct the support. Green ceramic tape is a ceramic tape that has not yet been fired (or sintered). Between any of these layers of green ceramic tape, a metallization made of a refractory metal is used to define the split ring resonator electrodes. This metallization can be patterned by screen printing, inkjet printing, or using any other typical HTCC metallization process. Multiple layers of green ceramic tape are stacked (the stacking process may employ one or more binders) and then fired at a temperature of approximately 1200°C to sinter the stacked materials and remove the binder. The result is a hermetically sealed antenna structure with a split ring conductor 110 encapsulated in a ceramic matrix, except for a single to the second side 102 of the ceramic matrix 150 (the side opposite the side where the plasma is generated) that extends through the support. outside of via connections. The hermetically sealed antenna structure is then polished in the area above the split ring conductor 110 to obtain the desired thickness of the ceramic matrix 150 between the first side and the split ring conductor 110 . The desired thickness of the ceramic matrix between the first side 101 and the open ring conductor 110 corresponds to the desired resonant frequency. In other words, the resonant frequency of the plasma generation device 100, 100A may be tuned or otherwise changed by changing the thickness of the ceramic matrix 150 between the top surface 130 of the first side 101 and the open ring conductor 110.

Turning now to Figures 10-12, another embodiment of a plasma generation device 800 is shown. In this embodiment, the plasma generation device 800 includes a dielectric support 818 having a process-facing side 801 or first side and a non-process side 802 or second side, the first side being exposed to the processing chamber 500 , the interior of cell chamber 408 or otherwise exposed to the semiconductor manufacturing process. The non-process facing side 802 includes antenna traces, resonators or conductor traces 810 deposited on a dielectric support 818 . In an embodiment, dielectric support 818 and conductor traces 810 are prepared by an HTCC process. As shown, conductor trace 810 has a split ring configuration defining gap 807, similar to other previously discussed embodiments. Conductor trace 810 is also connected to a connector 803 that provides power to plasma generation device 800, such as an RF connector. The non-process side 802 is positioned relative to the ground plane 860 such that a space 862 is defined between the ground plane 860 and the non-process side 802 of the support 818 . This space is typically and most conveniently filled with ambient air at atmospheric pressure as the dielectric, but other materials may be chosen to fill space 862 due to stability or increased breakdown voltage. In an embodiment, ground plane 860 is the ground reference for conductor trace 810 . Therefore, it is possible to adjust the resonant frequency of the conductor trace 810 by increasing or decreasing the space 862 defined between the ground plane 860 and the non-process side 802 of the support 818 . In an embodiment, this may be accomplished by moving ground plane 860 relative to support 818 . Space 862 may also be configured to stabilize the temperature of plasma generation device 800 to prevent shifting of the resonant frequency when plasma generation device 800 is operated.

The process side 801 of the support 818 includes a plurality of emitters 806, 808 (eg, two (2) emitters) constructed of aluminum. In embodiments, emitters 806, 808 may also be coated or partially coated with a thin layer of dielectric material to increase their inertness in the presence of semiconductor manufacturing processes. As shown, there are two emitters 806, 808 and they are positioned adjacent to each other defining a space or gap 817 between them. Each emitter 806 , 808 is connected to a conductor trace 810 on the non-process side 801 of the support 818 through a hermetically sealed via 805 . Thus, hermetically sealed via 805 connects emitters 806, 808 to conductor trace 810 across a pressure threshold. As shown, the emitters 806, 808 include a teardrop shape and are positioned such that a gap 817 is formed between the opposing tip portions of the emitters 806, 808. In other words, as shown in Figure 10, emitters 806, 808 are positioned on plane P as mirror images of each other.

In operation, the high electric field generated in the gap 817 between the emitters 806, 808 generates a plasma 400 similar to the previously described embodiment (Fig. 3A). However, because conductor trace 810 is positioned on the non-process side 802 of support 818, it does not need to be buried in a ceramic matrix, and therefore can be constructed of a better, more conductive material such as copper or silver. In embodiments, conductor 810 is prepared by conventional thick film and thin film processes and is not limited to low conductivity metals compatible with HTCC processes, such as tungsten.

While the present invention has been particularly shown and described with reference to certain exemplary embodiments, those skilled in the art will understand that other modifications may be made without departing from the spirit and scope of the invention, which is supported by the written description and drawings. Various changes in implementation details are included. Furthermore, where example embodiments are described with reference to a certain number of elements, it will be understood that the example embodiments may be practiced with fewer or more than the certain number of elements.

Claims (23)

1. A plasma generating apparatus for generating a plasma from one or more gases inside a chamber, the plasma generating apparatus comprising:

a support having a first side and an opposite second side, wherein the support comprises a ceramic matrix,

an open loop conductor embedded in the ceramic matrix,

a hermetically sealed via extending from the split ring conductor to the second side of the support and configured to be connected to a power source, an

A ground plane formed on the second side of the support member and

wherein a plasma is configured to be generated proximate to the first side of the support, and

wherein the support is configured to seal to a wall of the chamber such that the first side is exposed to the one or more gases inside the chamber and the second side is isolated from the plasma and the one or more gases inside the chamber.

2. The plasma generating apparatus according to claim 1, wherein the ceramic matrix is composed of Al ₂ O ₃ And at least one of AlN.

3. The plasma-generating device of claim 1, wherein the ceramic matrix is comprised of one or more materials compatible with the plasma and the one or more gases inside the chamber.

4. The plasma generation apparatus of claim 1, wherein the split ring conductor is comprised of a refractory metal.

5. The plasma-generating device of claim 1, further comprising at least one plasma-initiating electrode, each electrode comprising a hermetically sealed via extending through the ceramic matrix from the first side of the support to the second side of the support.

6. The plasma-generating device of claim 5, wherein the at least one starting electrode is comprised of a refractory metal.

7. The plasma generating apparatus of claim 5, wherein the plurality of starting electrodes are spaced apart from each other by a predetermined distance to enable starting of the plasma within a predetermined pressure range.

8. The plasma generating device of claim 1, further comprising a light collecting element spanning the ceramic matrix and the ground plane, wherein the light collecting element is configured to collect light emitted by the plasma and transmit the light through the ceramic matrix and the ground plane so as to be viewed from the second side of the support, wherein the light collecting element is hermetically sealed against the ceramic matrix.

9. The plasma generating device of claim 8, wherein the light collecting element is a lens positioned proximate to the split ring conductor, and wherein the lens comprises a curvature configured to optimize transmission of the light to an input field of view of one of: (1) an optical fiber; (2) an optical fiber bundle; and (3) a spectrometer.

10. A gas sensor, comprising:

a plasma generating device having a first side and an opposite second side, the plasma generating device comprising:

an open loop conductor surrounded by a ceramic matrix and configured to generate a plasma proximate the first side,

an optical element extending through the ceramic matrix between the first side and the second side, wherein the optical element is configured to collect light emitted by the plasma; and

a connector electrically connected to the split ring conductor,

wherein the optical element is hermetically sealed to the ceramic matrix using one of: (1) braze sealing; and (2) compression sealing.

11. The gas sensor of claim 10, wherein the connector is an antenna connector configured to receive RF energy from a cable, and wherein an optical fiber is connected to the optical element and configured to receive light collected by the optical element.

12. The gas sensor of claim 11, further comprising remote electronics configured to interact with the gas sensor through the cable and the optical fiber, wherein the operation occurs at a temperature greater than 120 ℃.

13. The gas sensor of claim 10, wherein the plasma generating device is configured to be exposed to one or more gases within a process chamber and to function as part of a wall of the process chamber.

14. The gas sensor of claim 10, further comprising a ground plane formed on the second side of the plasma-generating device.

15. The gas sensor of claim 10, wherein the split ring conductor is comprised of a refractory metal.

16. The gas sensor of claim 10, wherein the first side of the plasma-generating device comprises a polished surface.

17. A method of manufacturing a plasma-generating device, the method comprising:

forming a support from a ceramic matrix in a green state, wherein the support comprises a first side and an opposing second side;

embedding a split ring conductor and a hermetically sealed via in the ceramic matrix as the formed portion of the support, wherein the hermetically sealed via extends from the split ring conductor to the second side of the support;

Firing the ceramic matrix with the embedded split ring conductor;

positioning a ground plane proximate to the second side of the support either before or after the firing; and

the first side of the support is polished to obtain a desired thickness of ceramic matrix between the first side and the split ring conductor, wherein the desired thickness of the ceramic matrix corresponds to a desired resonant frequency.

18. A method of manufacturing a split-ring resonator plasma generating apparatus, the method comprising:

providing a plurality of ceramic tapes;

forming a pattern of at least one metallization on at least one of the plurality of ceramic tapes, wherein the pattern of at least one metallization comprises a split-ring resonator;

stacking the plurality of ceramic tapes;

firing the stack to produce a hermetically sealed antenna structure comprising open loop conductors in a ceramic matrix; and

the hermetically sealed antenna structure is polished in an area above the split ring conductor.

19. The method of claim 18, wherein one or more measurements of one or more characteristics of the antenna structure, such as resonant frequency, quality factor, and dielectric thickness, are used to determine an endpoint of the polishing.

20. The method of claim 18, further comprising adding an index mark to the same metallization pattern as the split ring conductor, wherein the index mark is exposed for guiding the polishing to a target thickness during a cutting process.

21. A gas sensing system, comprising:

a plasma generating apparatus, comprising:

a split-ring resonator microstrip comprising:

split ring conductor, and

a ceramic matrix configured to surround and support the split ring conductor; and

a temperature sensor in thermal communication with the plasma-generating device to determine a temperature of the plasma-generating device, wherein the temperature of the plasma-generating device is considered during operation of the gas sensing system.

22. The gas sensing system of claim 21, further comprising a heater in thermal communication with the plasma-generating device, wherein the heater and the temperature sensor are configured to control a temperature of the plasma-generating device.

23. A gas sensing system, comprising:

a plasma generating apparatus, comprising:

a split-ring resonator microstrip comprising:

split ring conductor, and

A ceramic matrix configured to support the split ring resonator microstrip, wherein the split ring conductor is embedded within the ceramic matrix; and

a dual connection flow-through gas cell defining a gas passage through a plasma chamber, wherein the gas cell comprises an optical window that is positioned substantially across the plasma chamber away from and parallel to the ceramic matrix of the plasma generating device,

wherein the gas unit is configured to provide a flow of gas in a direction substantially parallel to the plane of the plasma generating device and the plane of the optical window,

wherein the gas channel and the plasma chamber include features having a dimension in a direction substantially normal to the direction of gas flow of less than about 10 mm.